Standard evanescent mode bandpass filters are well-known in the art. These devices utilizes parallel resonators with inherent relatively large coupling for a given spacing.
In many applications, bridge coupled response has been found to be desirable and has been achieved in a folded evanescent structure at the expense of a relatively large size and added complexity. In other applications, it has been found desirable to shorten the length of an evanescent mode filter without utilizing the aforementioned folded design.
Extension descriptions of evanescnet mode filters are readily available in the literature and may be obtained by referring to such publications as, for example, an article entitled, "New Application of Evanescent Mode Waveguide to Filter Design," by Richard V. Snyder, in IEEE-MTT-25, December 1977, pages 1013-1021.